The present invention relates to a digital switching system.
Various types of switching systems have been proposed to perform circuit switching. In these systems, circuit switching is performed in response to service demand and a transparent transmission line is assured while the service demand call is set. Therefore, various types of implementation have been utilized in digital switching systems of circuit switching call type to transmit a great amount of data with the shortest possible predetermined transmission delay. In general, a small-capacity high-speed memory is used in a switching network section of such a system. A typical example is described in "Digital Data Switching Network", T. Arita et al., Vol. 28, Nos. 5-6, PP. 328-337, 1980, Nippon Telegraph and Telephone Public Corporation Musashino Electrical Communication Laboratory.
Along with the recent development of new data transmission systems such as telex and teletex, a switching system is developed to effectively use the transmission line when the density of transmission data is low. In this system, a message is broken up into smaller segments or packets for transmission onto the line in a packet switching network. This packet switching system is an example of a store-and-forward system, so that a message channel must have a large storage capacity. Conventionally, in order to perform packet switching as well in a circuit switching system, a packet switching system must be arranged together with the circuit switching system. However, when different systems (i.e., a circuit switching system and a message or store-and-forward system such as a packet switching system) are used, the number of component parts is increased, resulting in high cost. In addition, when the traffic condition changes, the available service is confined to the limit of each system. A total switching system having different types of system cannot thus provide flexible operations.